Method of testing while refining metals



Sept. 8, 1936. s. DEI TZ, JR.. ET AL METHOD OF TESTING WHILE REFINING METALS Filed May 15, 1935 FIG. 1.

FIG. 2.

lNVENTORS L. S. DE/TZ JR.

6. W. WHITNEY 7 ATTORNEK Patented Sept. 8, 1936 UNITED STATES PATENT OFFICE METHOD OF TESTING WHILE REFINING METALS York v Application May 15. 1935; Serial No. 21,538

I 12 Claims.

This invention relates to a method of testing while refining metals and more particularly to a method of testing antimoniferous alloys of lead while being refined.

In the manufacture of lead covered electrical conductor cables, particularly as used in the communications art, a seamless sheath of lead or lead alloy is formed on the cable by an extrusion process. This lead or lead,alloy must have cer- 'tain physical characteristics in order to be extruded satisfactorily as a continuous and substantially uniform sheath, and these physical characteristics are dependent upon the chemical composition of the sheathing material. In particular, certain alloys comprising principally lead with a content of antimony from about 0.50% to about 1.50% are found to be capable of being extruded satisfactorily and of forming a relatively tough, flexible and wear and corrosion resistant sheath, provided that tin, zinc and cadmium are present in amounts less than .005% each and preferably less than .002% each.

It is common practice to employ sheathing materials made of metals obtained by refining old or discarded cable sheaths. Many of the old cable sheaths were made of lead alloys containing substantial quantities of tin and other, elements, and in addition .manycable sheaths have joints or repairs made therein with solder or other tin bearing materials, which are included in the scrap metals obtained therefrom. A proportion also of the raw lead which may be available for the manufacture of the lead-antimony alloys may carry tin, cadmiumand zinc in amounts well above .005%. In the practice of any method of refining lead-antimony alloys to remove tin, cadmium and zinc, it is of great advantage to have a simple, rapid and accurate method of testing the material while being refined to learn whether asuitable degree of purity has been attained. a

An object of the present invention is to provide a method of. testing metals while in the process of being refined, which is accurate and reliable in use.

An embodiment of the invention comprises the casting of small test specimens taken at'intervals during the refining of lead carrying approximately 1% antimony and the observation of crystalline flakes or facets spontaneously formed on a free surface of the test bars. These flakes or facets, or some of them, change sharply from a frosted pewter like a pearance to a brilliantly polished mirror surface as soon as the tin. Pa!- mium and zinc content of the alloy falls below an amount harmful to the use of the alloy in an extrusion process.

Other objects and features of the invention will appear from the following detailed description of one' embodiment thereof taken in connection with the accompanying drawing, in which the same reference numerals are applied to identical parts in the several figures and in which Fig. 1 is a plan view of a bar; 4 a

Fig. 2 is a side view thereof, and

Fig. 3 is a. perspective view on a smaller scale of a test bar mold withtwoi test bars therein.

In order to describe the embodiment of the invention herein disclosed, it will be necessary to describe one of the methods of refining leadantimony with which the present invention may be coupled in use. However, the present invention.- is not limited to the particular method of refining with which it is illustrated but may be coupled with others equally well.

Assuming that a quantity of material comprising mainly lead with approximately 1% antimony and carrying tin, cadmium and zinc as impurities in amounts considerably greater than 005% each, say for example, .02% .tin, .0l% cadmium and .01% zinc, which is representative of material upon which the invention has been satisfactorily practiced, the material is melted down, preferably in an externally fired pot furnace. It is brought to a suitable temperature wedge shaped test simultaneously blown through the molten mass. A certain amount of lead oxide dross forms on the surface and is skimmed 011. The tin, cadmium and zinc impurities in the charge are oxidized and carried into the dross.

Toward the end of the time which experience shows is necessary for the'refining of. the particular material in question and which is ordinarily a matter of eight to twenty-four hours, the furnace attendant begins casting a sequence of test specimens such as indicated at Ill in the drawing. This may be conveniently done by taking metal from the pot with a small hand ladle and pouring it intoa small test mold II. The mold may be a flat rectangular block of iron having one or more rectangularly elongated recesses 12 formed therein. The mold may be laid on the floor vor any suitable horizontal surface and tilted slightly from the horizontal as shown in Fig. '3 by a prop l3 of any convenient material and form.

- and the charge is stirred mechanically and air is Test specimensthus cast will have the gen- 5 tually more or less interpenetrant clusters.

These facets are well known, their characteristic feature being a frosted surface of pewter like color, bright but in no sense polished in appearance.

At some definite point in the continued refining of the metal, a new kind of flake or facet l6 appears on the surface l4. These are triangles 16 generally similar in size, shape and distribution to the triangles l5, apparently a little more apt to be completely independent of each other. These flakes are brilliantly smooth and bright, like a highly polished mirror, extremely distinctive in appearance, and are unmistakable. They never appear until the metal has attained substantially the minimum purity required for smooth accurate extrusion as a continuous, tough and satisfactorily flexible cable sheath.

The chemical composition and the crystal structure of these mirror like or specular facets or flakes is not as yet known, but it is certain that they do not appear until tin, cadmium and zinc or any one or two of these have been. reduced to less than .005%, which means to an amount where they do not affect the material adversely with respect to its extrusion characteristics. It also appears to be certain that the appearance on the test bars of these mirror bright or specular flakes is a reliable indication that the desired degree of purity has been reached. Thus the appearance of specular flakes is a simple, rapid, accurate and convenient test for the degree of purity of leadantimony alloy requisite for extrusion purposes,

indicating that tin, cadmium and zinc have each been reduced to less than .005%.

Although the test specimens'are herein shown as wedge shaped bars, this is merely for convenience"as such pieces are easily removed from, the form of. mold shown. The test pieces may be complete bars poured in the same mold in a levelv position, or may be poured in any other form of mold, or even may be .merely thin' pancakes poured on a smooth level surface. It is only essential that the test piece have a sizable free surface and be poured on or in a prewarmed mold so that it will not set toorapidly and so prevent the development of specular flakes. Although the method of refining herein disclosed is essentially that of oxidizing impurities by simultaneous-mechanical agitation and blowing with air, the invention is equally applicable to other modes of purification. For example, the

lead-antimony alloy may also be melted, covered with molten caustic soda and agitated while adding successive portions of an oxidizing agent such as sodium nitrate to oxidize tin, cadmium and zinc. In another method disclosed and claimed in copending application Serial No. 21,539 filed May 15, 1935 by Louis S. Deitz, Jr., one of. the present inventors, the molten alloy is heated with copper which dissolves therein at a relatively high temperature, whereupon the temperature of the alloy is lowered and the copper is precipitated out-in the dross formed, bringing with it tin,

cadmium and zinc. The present invention consists essentially in removing tin, cadmium and zinc by any satisfactory procedure from molten crude lead-antimony alloy until what may be termed the specular condition is attained when test specimens of the alloy show the brilliantly polished, mirror like or specular flakes which indicate that the alloy is sufliciently free from tin, cadmium and zinc to be satisfactory for extrusion purposes, i. e. that none of these three impurities is present in an amount exceeding .005%.

The embodiment of the invention herein disclosed is illustrative merely and may be modified and departed from in many ways without departing from the spirit and scope of the invention as pointed out in and limited solely by the appended claims.

What is claimed is:

1. A method of refining antimoniferous lead which comprises a testing step of forming a sequence of test specimens until mirror bright flakes appear upon a free surface thereof on setting. 2. The method of purifying antimoniferous lead which comprises refining the molten material until test specimens cast with a free surface show specular facets on the free surface.

3. In a method of refining antimoniferous lead the steps of casting a test specimen having a free surface and inspecting the free surface for mirror bright spots spontaneously formed thereon.

4. The method of testing antimoniferous lead to show the absence of tin, cadmium and zinc in amounts exceeding .005% each which comprises inspecting a free surface of a cast test specimen for mirror bright spontaneously formed spots thereon.

5. The method of testing antimoniferous lead to show the suitability of the material for use in extruding cable sheaths therefrom which comprises inspecting a free surface of a cast test specimen for mirror bright spontaneously formed spots thereon.

6. The method of purifying lead antimony alloys, which comprises treating a lead antimony alloy in the molten state with a reagent capable of removing impurities therefrom, continuing the treatment until a free surface of a test specimen cast from the alloy exhibits a plurality of mirror bright spontaneously formed areas thereon, and then casting the alloy.

'7. The method of purifying lead antimony alloys for use in manufacturing extruded cable sheathing, which comprises treating a lead antimony alloy in the molten state with a reagent capable of removing tin, cadmium and zinc, continuing the treatment until a free surface of a test specimen cast from.the alloy exhibits a plurality of mirror bright spontaneously formed areas thereon, and then casting the alloy.

8. The method of purifying lead-antimony alloys containing from about .5% to about 1.5% of antimony, which comprises treating the lead to remove impurities therefrom, casting small test specimens thereof at intervals during the treatment until a free surface of a specimen exhibits a plurality of mirror bright spontaneously formed areas thereon, and then stopping the purifying treatment.

9. The method of purifying lead-antimony alloys containing. from about .5% to about 1.5% of antimony, which comprises treating the lead to remove tin, cadmium and zinc therefrom, casting small test specimens thereof at intervals during the treatment until a free surface of a specimen exhibits a plurality of mirror bright spontaneously formed areas thereon, and then stopping the purifying treatment.

10. The method of purifying lead antimony a1- loys containing from about 0.5% to about 1.5% antimony which comprises refining the molten material until test specimens cast with a free surface show specular facets on the free surface.

11. The method of purifying lead antimony alloys containing from about 0.5% to about 1.5% antimony, which comprises treating such a lead antimony alloy in the molten state with a reagent capable of removing impurities therefrom, continuing the treatment until a free surface of a test specimen cast from the alloy exhibits a piurality of mirror bright spontaneously formed areas thereon, and then casting the alloy.

12. The method of purifying lead antimony a1- loys containing from about 0.5% to about 1.5%

antimony for use in manufacturing extruded cable sheathing, which comprises treating such a lead antimony alloy in the molten state with a reagent capable of removing tin, cadmium and zinc, continuing the treatment until a free surface of a test specimen cast from the alloyexhibits a plurality of mirror bright spontaneously formed areas thereon, and then casting the alloy.

.LOUIS S. DEITZ, JR.

GEORGE W. WHITNEY. 

